An example of a multibeam antenna is disclosed in, for example, Japanese unexamined patent publication No. HEI 5-191139 published on Jul. 30, 1993. The antenna disclosed in this publication includes two primary radiators disposed to radiate beams to the same point on an offset paraboloidal reflector of the antenna. In this antenna, an axis passing through the aperture center of the paraboloidal reflector and paralleling the parabola axis of the reflector is defined as a beam axis of the paraboloidal reflector. One of the two primary reflectors is located at the focal point of the reflector, and the other radiator is located on the beam axis. The angle between the line passing through the aperture center and the focal point of the reflector and the parabola axis is defined as a tilt angle. The tilt angle is from 1 to 1.4 times a desired beam width.
A reflector meeting the above-stated condition cannot be a versatile reflector, but it can only reflect a beam in or from a specific direction. Recently, satellite communications and satellite broadcasting are common. Accordingly, parabolic antennas which can be used only single satellites are not desirable in manufacturing cost. In addition, in this type of paraboloidal reflectors, aberration due to displaced feeding is minimized under some specific conditions, which results in a large focal-length-to-aperture ratio, F/D, of the paraboloidal reflector.
Therefore, an object of the present invention is to provide a versatile reflector for a multibeam antenna which has a similar size to an ordinary paraboloidal reflector.